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Old 10-03-2022, 07:00 PM #1
Ducksrus Ducksrus is offline
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'03 Brake Booster Squeal

Have a squeal or sound like a loud buzzer coming from brake booster system after 3-4 presses of brake, more so when cold. This sound is in addition to the normal hum of the booster motor. Majority of people with similar issues indicated to replace booster motor. Replaced motor w/a new unit; however, no change in the buzzing/squealing. So think that the issue may be pump, not sure.

Has anyone repaired &/or rebuilt a brake booster pump? Is there such thing as a rebuild kit for the pump? Can find used motor & pump, not just a working pump.

Below are links to recordings of the sound coming from brake booster system, both inside & under hood of truck.
4RNR1 - YouTube
4RNR3 - YouTube

Tks

Last edited by Ducksrus; 10-15-2022 at 07:13 AM.
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Old 10-15-2022, 06:09 PM #2
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Replaced piston & o-ring on accumulator to hopefully stop the squeal & improve brake performance. Brakes feel & function better, but squeal not affected. The sound cycles now every 4-5 seconds when brakes pushed instead of being sporadic. Still could be from pump, just not sure.
If not from pump, is there a relay in the MC controls that could possibly be failing?
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Old 10-18-2022, 05:59 PM #3
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My 2008 started this a while back. I think I read every thread on the internet about it. Some had luck replacing the o-ring and accumulator, some had luck rebuilding the motor, some had no luck with those fixes and ended up replacing the entire MC and booster assembly. After my research, I decided to replace the entire assembly. I still don't have a good place for a rebuild like that and I don't want to chance anything when it comes to the brake system and most importantly, my daughter will be driving my 4runner most of the time now. Can't take a chance on that!

It wasn't cheap but replacing the entire assembly was fairly quick vs a questionable rebuild. The squeal is gone and the brakes feel as good as new.
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Old 10-20-2022, 05:40 PM #4
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Yes, replacing unit would have been the correct option, but that is hindsight. Thanks for responding
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